Looking at the range of it I see why it's on the threatened species list, because it's only around Florida, so much like Bangaii cardinals they're threatened because they don't exist other places.
That said I wonder if it's a non-photosythetic filter feeder, just by the shape of those polyps looks like they're primarily grabbing stuff out of the water column, are there any NPS branching stony corals though? I mean I know sun corals make a hard base.